One of the last operations performed on an automobile before it rolls off the production line is adjusting the tension of the manual parking brake system. Properly adjusting the parking brake system is of great importance for several reasons. First is safety. If a parking brake system is improperly adjusted, a vehicle operator may have a false sense of security regarding the effectiveness of the park brake system. For example, when the employee drives the automobile off the production line, he or she will typically engage the manual parking brake once they park the automobile in the storage lot. If the parking brake is set too loose, the automobile may begin to unintentionally roll from its stationary position, thereby posing a potential threat to the safety of the employee, the condition of the automobile, other automobiles within the storage lot, and the production facility. Moreover, this sense of security will flow to the consumer, who, as a result of an improperly tensioned parking brake system, may be at risk of personal injury, the injury of others, or the injury of property.
Second, the proper tensioning of the parking brake system creates a perception of quality to the consumer. If the tension of the parking brake is set appropriately, the consumer will regard this as an indication of high build quality. If the tension of the parking brake, however, is improperly set, the potential consumer may view this as a sign of poor vehicle refinement. This is especially true of high performance vehicles such as the Mustang, manufactured by the Ford Motor Company, of Dearborn, Mich.
Unfortunately, the cables of a parking brake system are inherently difficult to tension properly, particularly in a production environment that is accustomed to using torque specifications for securing fasteners. The typical tools used for adjusting to a given torque specification include pneumatic wrenches or direct-current (DC) electrical wrenches. These tools have proven to be capable of tightening to the design specifications of a vehicle. The threaded rod and the adjustment nut seen in many cable tensioning systems, however, do not experience the typical clamp loads and require very little torque to be adjusted properly.
Current efforts to adjust the tensioning of the parking brake are to use a torque wrench to tighten the adjustment nut attached to the end of the cable. The torque wrench is set with a predefined torque specification and the adjustment nut is tightened until the desired torque is achieved. This adjustment strategy has several shortcomings for tightening a cable system such as those seen in vehicle parking brakes. First, merely setting the torque on the adjustment nut may result in wide variations cable tension from one automobile to another. For example, the parking brake tension of one automobile may have the predefined torque specification as low as 1.9 Newton-meters (N-m), which is well below the lower limit for reliable operation of the operation of conventional pneumatic tools. As a result, the need of a power or electrical wrench is usually necessary. Another shortcoming is that the prevailing torque on the fastener is highly variable due to the manufacturing tolerances and environmental conditions, which can drastically alter the required torque to properly adjust the parking brake. Combined with such a low torque specification, it is nearly impossible to set a torque target that matches the desired cable tension.
Problems commonly arise without proper parking brake adjustment. Under-tension is one problem that can result by improperly adjusting a parking brake. If a parking brake system is under-tensioned, the parking brake will have free-play. Free-play is where the handle of the parking brake can be pulled some distance before any tension is applied to the parking brake cable. This looseness in the system is perceived by the customer as an indicator of poor build quality. In extreme cases, this can cause an operator of the vehicle to believe the vehicle is properly secured after applying the parking brake, where the brake is actually not yet engaged. Conversely, over-tension is another result of improper parking brake adjustment. In an over-tension system, the parking brake may be applied when the operator believes the parking brake is disengaged. The parking brake cable may apply brake pressure at the wheels of the vehicle, while the parking brake is in the rest position. As a result of over-tension, brake drag is created. Brake drag causes quality and safety concerns, since it can cause accelerated brake wear, and also overheating at the vehicle's wheels.
Therefore, an apparatus, method, and system for properly tensioning a parking brake without relying on a torque specification is needed to ensure quality production.